fireplace removal

Hi all, I have some builders in at the moment to remove my chimney breast, now I am no expert and it looks like they have done a good job, but my front bedroom and rear bedroom used to have a fireplace that was bricked up. The builders knew this and part of the quote was to remove the bricked...

Please could someone advise me as to if it’s okay to remove the base of a fireplace. Please find pictures attached. It looks like at some point a concrete base has been put in but I wouldn’t want to risk removing it if it’s structural. Looking to build a hearth into it but I’d need to lower...